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TEST INSTRUMENT SAFETY
Normal use of test equipment exposes you to a certain
amount of danger from electrical shock because testing
must sometimes be performed where exposed voltage is
present. An electrical shock causing 10 milliamps of
current to pass through the heart will stop most human
heartbeats. Voltage as low as 35 volts dc or ac rms should
be considered dangerous and hazardous since it can
produce a lethal current under certain conditions. Higher
voltages pose an even greater threat because such voltage
can more easily produce a lethal current. Your normal
work habits should include all accepted practices to
prevent contact with exposed high voltage, and to steer
current away from your heart in case of accidental contact
with a high voltage. You will significantly reduce the risk
factor if you know and observe the following safety
precautions:
6. Some equipment with a two-wire ac power cord,
including some with polarized power plugs, is the
“hot chassis” type. This includes most recent
television receivers and audio equipment. A plastic or
wooden cabinet insulates the chassis to protect the
customer. When the cabinet is removed for servicing,
a serious shock hazard exists if the chassis is touched.
Not only does this present a dangerous shock hazard,
but damage to test instruments or the equipment under
test may result from connecting the ground lead of
most test instruments to a “hot chassis”. To test “hot
chassis” equipment, always connect an isolation
transformer between the ac outlet and the equipment
under test. The B+K Precision Model TR-110
Isolation Transformer, or Model 1653A or 1655A AC
Power Supply is suitable for most applications. To be
on the safe side, treat all two-wire ac equipment as
“hot-chassis” unless you are sure it has an isolated
chassis or an earth ground chassis.
1. Don’t expose high voltage needlessly. Remove
housings and covers only when necessary. Turn off
equipment while making test connections in highvoltage circuits. Discharge high-voltage capacitors
after removing power.
7. On test instruments or any equipment with a 3-wire ac
power plug, use only a 3-wire outlet. This is a safety
feature to keep the housing or other exposed elements
at earth ground.
2. If possible, familiarize yourself with the equipment
being tested and the location of its high voltage
points. However, remember that high voltage may
appear at unexpected points in defective equipment.
8. B+K Precision products are not authorized for use in
any application involving direct contact between our
product and the human body, or for use as a critical
component in a life support device or system. Here,
“direct contact” refers to any connection from or to
our equipment via any cabling or switching means. A
“critical component” is any component of a life
support device or system whose failure to perform can
be reasonably expected to cause failure of that device
or system, or to affect its safety or effectiveness.
3. Use an insulated floor material or a large, insulated
floor mat to stand on, and an insulated work surface
on which to place equipment; and make certain such
surfaces are not damp or wet.
4. Use the time proven “one hand in the pocket”
technique while handling an instrument probe. Be
particularly careful to avoid contacting a nearby
metal object that could provide a good ground return
path.
9. Never work alone. Someone should be nearby to
render aid if necessary. Training in CPR (cardiopulmonary resuscitation) first aid is highly
recommended.
5. When testing ac powered equipment, remember that
ac line voltage is usually present on some power
input circuits such as the on-off switch, fuses, power
transformer, etc. any time the equipment is connected
to an ac outlet, even if the equipment is turned off.
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